#1 I'd check your negative battery terminal ground wire where it is attached to the body just beside the battery. If that looks rusty and such take it off clean it all up, so any or all corrosion is gone and re-bolt everything cleaned up to the clean metal. IF that doesn't work check the actual exposed copper battery wire in the terminals and at the ground as that can degrade over time but it can be hidden inside the connector or even under the wire insulation as the decay has worked it's way up. In my experience with numerous cars things going totally screwy when you turn the key can be a sign of bad connections and wires at the battery terminals and the main ground. And it can happen in an instant when the flow of amps degrades to a point that all of a sudden nothing works on start-up. You can put a voltmeter on the battery or with the key in the run position stick a voltmeter into the cigarette lighter and it will read 12V+ but it's not about voltage with no load... It's about delivering that voltage with the amps that are required to start the car. Since you turn the key and everything goes to crap that tells me the first thing to check is degraded connections on the battery terminals, wires or the ground..